Apparatus for the automatic spraying of coatings on objects



Nov. 29, 1960 Q. L. WRUCK APPARATUS FOR THE AUTOMATIC SPRAYING OF COATINGS ON OBJECTS Filed Oct. 4, 1957 5 Sheets-Sheet l PHOTO RELAY TIME DELAY cIRcuIT CELL CIRC'UIT l 68 I I I 25 l THRESHOLD 75 TIME DELAY CONTROL ADJUST INVENTOR VALVE\ 74 QUAYNE L.WRUCK BY dmw gIfi/zf TO SPRAY AIR g mw m NOZZLE SUPPLY ATTORNEY Nov. 29-, 1960 Q. 1 WRUCK 2,961,990

APPARATUS FOR'THE AUTOMATIC SPRAYING OF COATINGS ON OBJECTS Filed Oct. 4, 1957 5 Sheets-Sheet z ATTORNEY Nov. 29, 1960 Q. WRUCK 2,961,990

APPARATUS FOR THE} AUTOMATIC SPRAYING OF COATINGS ON OBJECTS Filed Oct. 4, 1957 5 Sheets-Sheet 3 b, :REG/U/ C,

INVENTOR QUAYNE L.WRUCK BY g "47 ,6490%,

ATTORNEY Q. L. WRUCK Nov. 29, 1960 APPARATUS FOR THE AUTOMATIC SPRAYING OF COATINGS ON OBJECTS Filed Oct. 4, 1957 5 Sheets-Sheet 5 N ZOTCmOQ W aw ATTORNEY APPARATUS FOR THE AUTOMATIC SPRAYING OF COATINGS N OBJECTS Quayne L. Wruck, Greenfield, Wis., assignor to Allen- Bradley Company, Milwaukee, Wis., a corporation of Wisconsin Filed Oct. 4, 1957, Ser. No. 688,181

Claims. (Cl. 118-2) 7 This invention relates to the automatic spraying of coatings upon objects and discloses as an exemplary embodiment a control for a paint spray nozzle in which the nozzle is operative only when continuously conveyed objects are within the range of the paint spray cone emitted from the nozzle, such control being applicable to a wide range of sizes of objects and spray booths.

The automatic painting of objects has long been recognized as desirable because of the uniformity of results that can be obtained and because of the cost saving resulting from reduced labor and paint costs. Heretofore, automatic paint spraying has been generally approached with reference to specific, generally uniform objects and the spraying equipment utilized has been adapted for a particular spraying application. This approach has not solved the more general problem of spraying objects of various sizes, or objects that are spaced at varying intervals along a conveyor or other means for moving them past the paint spray station. Hence, it is a principal object of this invention to provide a packaged apparatus which may be installed in spray booths of various proportions and which effects maximum economy of paint consumption irrespective of the size of the objects being painted and irrespective of the spacing of such objects along conveying apparatus.

The use of photoelectric responsive devices to control mechanisms is well-known and in their classical arrangement a light source is arranged to fall upon the photoelectric device and a signal is developed by the interruption of the light beam as objects pass therethrough. Such an arrangement is not practical for paint spray control because the location of either the light source or the photoelectric responsive device in a position in which the light beam is interrupted by passing objects exposes one of these devices to Spindrift paint in the operative area of the spray booth. This difliculty can be met by 10- cating the light transmitting and receiving units outside of the spray booth, but such an arrangement necessarily disposes these elements at some considerable distance from the paint spray nozzle and hence requires a long time delay between the development of the signal and the actuation of the spray nozzle, which time delay arrangements are complicated, expensive and subject to failure. It is, accordingly, an object of this invention to locate the transmitting and receiving units in close proximity to the paint spray nozzle, but removed from the operative area of the spray booth so that these units do not become contaminated with paint. Ancillary to this object, it is a further object of this invention to utilize incident or reflected light in the control system rather than transmitted light, and to dispose the light transmitting and receiving elements so that signals are developed only due to the presence of objects to be painted and not by false reflections from the spray booth itself or other material within the booth.

One type of so-called automatic painting apparatus -utilizes one or. more spraynozzles operating'continu- Unit Stat Pa fltfo ously and adjusted so as to cover objects passing through the spray booth. This type of installation suflices where the objects to be painted are of the same or relatively similar dimensions, but obviously, such a system must be adjusted to adequately cover the largest of the objects to be painted. One of the objects of this invention is to provide control for multiple spray nozzles whereby each of the nozzles operates only if there is an object present within its coverage area.

A still further object of the invention is to provide a control mechanism which will ensure the even applica tion of paint, with minimum waste.

Further objects and advantages of the invention will be apparent from the following detailed description and from the attached drawings, in which:

Fig. 1 is a perspective view of a paint spray booth showing the general arrangement of the conveying, spraying and light transmitting and receiving elements of the control system;

Fig. 2 is a plan view of a paint spray nozzle and its associated control system light transmitting and receiving units, and also illustrates the relative positions of the aforesaid items with reference to objects to be painted and the rear wall of the spray booth;

Fig. 3 is a sectional view on the plane indicated by line 3-3 of Fig. 2 showing the vertical orientation of a pair of signal receiving units disposed to adapt the apparatus to objects of various vertical heights;

Fig. 4 is a sectional view on the plane indicated by line 4-4 in Fig. 2 showing the vertical arrangement of a pair of paint spray nozzles which may be actuated by the signal receiving devices of Fig. 3;

Fig. 5 is a sectional view on the plane indicated by line 5-5 in Fig. 4 and shows the vertical arrangement of the signal transmitting and receiving means and paint spray nozzles as viewed from an object being conveyed past the paint spray station;

Fig. 6 is an elevational view of an alternate embodiment of the invention illustrating a control in which the signal transmitting and receiving elements are oscillated so as to scan in a vertical plane;

Fig. 7 is a top plan view of the embodiment illustrated in Fig. 6;

Fig. 8 is a block diagram representing the electrical components of the control mechanism for the embodiment of Figs. 1-5, and

Fig. 9 is a block diagram illustrating an alternate control mechanism for the embodiment of Figs. 6 and 7.

According to the embodiment illustrated in Figs. 1 through 5, the signal or light transmitting and receiving units of the control mechanism are fixed and, for purposes of illustration, a pair of these units have been i1- lustrated in vertical juxtaposition, each of which controls the operation of one of a pair of paint spray nozzles arranged in similar vertical juxtaposition. The embodiment of Figs. 6, 7 and 9 is an alternate arrangement in which a single signal transmitting and receiving unit is utilized to control one or both of a pair of paint spray nozzles in vertical juxtaposition. The embodiments selected for illustration are exemplary of the invention and should be construed as illustrative thereof rather than as limitations of the specific means to be utilized in practicing the invention.

Referring to the details of the drawings, Fig. 1 illustrates in perspective a paint spray booth 11 having top and bottom walls 12 and 13, respectively, and front and back walls 14 and 15, respectively. An overhead trolley conveyor 16 passes medially through the spray booth adjacent the top 12 thereof and is provided with laterally spaced hangers 20 to which objects 21 may be secured. As illustrated, the objects 21 may be of various sizes and shapes, and, if desired, objects may be suspended in tandem by means of hooks 22. While for purposes of iilustration each conveyor hanger 20 has been shown carrying an object, it should be understood that the control mechanism to be described may be operated with equal advantage even though there are long vacant spaces along conveyor 16 which contain no objects. The conveyor operates in the direction shown by the arrow in Fig. 1 to move objects suspended therefrom continuously and preferably at a relatively uniform speed through the booth 11.

Adjacent the front wall of the booth is an upright supporting member 23 to which are aflixed a pair of light sources 24, connected to a suitable source of energy by cables 25.

Adjacent upright 23, but spaced longitudinally therefrom in the direction of conveyor run, is a receiver stand 29 to which are afiixed a pair of light receiver units 30, which are disposed to intercept light reflected from the beams emitted from light sources 24 as more particularly described hereafter. The receiver units 30 are connected with a control mechanism, not illustrated, by means of cables 31. It may be noted that stand 29, which rests upon the floor 13 of the spray booth, supports upright 23 by means of a pair of horizontal arms 35.

Longitudinally spaced from the receiver stand in the direction of conveyor travel, and supported by the stand through a second pair of horizontal arms 36 is a nozzle upright support 32 to which are affixed a pair of paint spray nozzles 33 directed to throw a pair of generally cone shaped mists of paint upon objects 21 as they pass through the coverage area of the paint mist. The nozzles 33 are supplied with pneumatic pressure and paint through flexible conduits 34.

The stand 29, arms 35 and 36 and uprights 23 and 32 form a rigid mounting structure which may be moved unitarily for adjustment of the area of paint coverage. Adjustment of the spacing of the uprights 23 and 32 from stand 29 is provided by slip couplings at 37, which may be tightened by set screws not shown.

Fig. 2 is a plan view looking downward from adjacent the top of the spray booth of Fig. l and may be oriented therewith by reference to the back wall 15 of the spray booth, light source 24, receiver unit 30 and nozzle 33. Referring to the details of Fig. 2, it may be seen that light source 24 may be adjusted vertically and pivoted horizontally on its upright 23 by means of a set screw 38. Angular adjustment for elevation or declination of the light beam 39 is further provided by a pivot 40. It may be observed that the light source 24 is selected to have a relatively narrow and nondivergent beam 39 in a horizontal plane. The light beam 39 is set so as to shine angularly toward object 21, the angle of inclination being in the direction of motion of said object.

Adjacent the light source and displaced longitudinally in the direction of the objects motion is a receiver unit 30, which may be adjusted vertically and pivotally on its stand 29 by means of a set screw 41. The receiver unit 30 comprises a closed box 42 containing a photoelectric responsive unit 43 and having a narrow port 46 for the admission of light falling within the region bounded by dotted lines 45. As may be observed, in Fig. 2, the light receiving port 46 is disposed so as to scan the approximate center of light beam 39 at its plane of intersection with object 21. It will be apparent from reference to Fig. 2 that an object placed in any vertical plane between forward point 47 and rearward point 48 will reflect light from beam 39 into the scanning region of receiver unit 30 and cause an increase in the light level falling upon photo-responsive device 43. It is also apparent that a signal will be transmitted to the light receiver unit 30 when the object 21 of Fig.

-2 reachespoint 49 along its path of travel and such signal will be maintained until the trailing edge of object 21 has passed the point 50 along its path of travel.

Fig. 2 further illustrates an object 21 being subjected to a mist or spray cone of paint 51 emitted from nozzle 33. Vertical and pivotal adjustment of nozzle 33 on its upright 32 is provided by means of a set screw 55.

Referring now to Fig. 3, further details of light receiver 30 are illustrated together with the vertical orientation of a pair of such units. In addition to previously mentioned box 42, photo-responsive device 43 and light port 46, it may be seen that the port 46 comprises an outer slit-like opening 52 and a smaller inner opening 56 disposed in close proximity to a sensitive portion of light responsive device 43. The vertical distance scanned by receiver 30 may be adjusted by a pair of set screws 57, threaded into a bellows or extension 58 forming a part of the light port.

Fig. 3 illustrates a pair of identical receiver units mounted in vertical juxtaposition on stand 29 and having their ports adjusted so that each scans approximately one-half of the vertical distance 59 representing the maximum height of an object or tandem mounted objects that may be accommodated with the illustrated adjustment of the receiver units. It is apparent by reference to Fig. 3 that with objects in the position shown, both receiver units 30 will be operative if light is reflected into them from the illustrated pair of objects 21. For this purpose, a pair of light sources 24, casting vertically divergent beams indicated by the dot-dash lines 60, may be employed. In the event that the lower object 21 were omitted, no signal would be received by lower receiver unit 30 and, as will be shown later, paint would not be sprayed into the area scanned by lower receiver unit 30; conversely the lower receiver unit 30 may be actuated while the upper remains idle. Similarly, when blank spaces on the conveyor are before both of the receiver units 30 no signal is received and neither of the spray nozzles are actuated.

By reference to'Fig. 2, it may be seen that the narrow horizontal area 53 scanned by receiver unit 30 across the plane of the back 15 of the spray booth 11 does not coincide with the impingement of light beam 39 upon the back of the booth, and thusno false signal is received from this reflecting surface. The location of the back of the booth is, therefore, in part, determinative of the adjustment of light sources 24 and receivers 30.

Fig. 4 illustrates the vertical arrangement of a pair of paint spray nozzles 33 on their upright 32. It may be seen thatpaint for the nozzles is supplied along a conduit or tube 64 from a source not illustrated and that pneumatic'pressure for the creation of a paint mist is supplied through a pair of tubes 65 supplied by flexible conduits 2-4 from a compressed air source not illustrated. The nozzles are preferably arranged to cast spray cones 51 which just meet at their adjacent boundaries, as at 54, and which cover a vertical distance coextensive with the vertical distance scanned by each receiver unit (see Fig. 3). vThus, each nozzle may be actuated independently by a separate light transmitter and receiver unit so that paint is applied only if .an object is present within the area covered by that paint spray cone.

Fig. '5 illustrates the arrangement of the light transmitting and receiving units and the spray nozzles as viewed from an object passing along the conveyor. By suitable vertical and angular adjustment of the units an arrangement maybe obtained which will initiate either or both of .a pair of spray nozzles when an object moving along the conveyor reaches the operative area covered by a spray cone, and similarly a nozzle may be extinguished or have its spray terminated when the object has moved beyond its operative range.

A block diagram illustrating the control mechanism for the spray nozzles is'shown in Fig. 8. When a signal, in the form ofiin'cident or reflected light from an object as scanned byqa. receiver unit 30, reaches photocell .43, the

1 energy developed therein is passed through cable -25 to a relay actuating control unit 66, the details of which are Well-known in the art and are not illustrated herein.

photocell 43 and thus to close an electrical relay. A

.'threshold control 67 (a variable bias resistance, for example) may be employed to control the sensitivity of the relay circuit so that it will discriminate against stray light which might strike photocell 43 and respond only to intended signals. The relay circuit 66 is connected through a time delay circuit 68 by means of connection 69 and .thence through connection 73 to a solenoid valve 74in the air supply lines to the spray nozzles. The details of the time delay circuit 68 are not shown as such devices are well-known in the art. It may comprise, for example, a condenser arranged to discharge through an adjustable resistance; Such an adjustment is shown functionally at 75. The time delay circuit operates to hold valve 74 open after relaycircuit 66 has stopped supplying a signal 7, so that paint spraying may continue after an object has moved beyond the area in which light is reflected into photocell 43. By a proper adjustment of the control 75, and coordination with the speed of operation of the conveyor, the emission of paint may be continued until an object has just left the operative area of the paint sprays, thus ensuring complete passage of each object through the paint mist and, therefore, equal application of paint.

The numerous adjustments provided for the framework upon which the light transmitters and receivers and nozzles are mounted, and the adjustments provided as a part of those elements, cooperate to permit universal application to various sizes of paint booths and objects. Thus, the system is a truly packaged unit of universal applir cation.

Fig. 6 illustrates in vertical elevation an alternate embodiment of the invention in which a single light source 24 is oscillated in a vertical plane from a lower position previously explained in detail, the light beam 39' is disposed to converge with the area scanned by light port 78 across the plane in which objects pass, as illustrated by dash-dot lines in Fig. 6. With light beam 39' and the area scanned by tube 78 angularly disposed, as shown,

at the plane of the back 15' of the spray booth, the light impinges upon an area out of the field of view of the port 78 so that signals are not reflected from this surface into the receiver unit 30', which contains the photocell.

'Fig. 7 illustrates further details of the alternate embodiment of Fig. 6, and it may be seen that the oscillating light transmitter-receiver unit is mounted upon upright '32 by a bracket 70 having a set screw 71 for clamping. 'The nozzles 33 are mounted adjustably as in the previously described embodiment, and clamped by said set screws 55'.

Thus, this embodiment has the same universal application features as those described in con- .nection with the embodiment of Figs. 1-5.

In the Fig. 6 and 7 embodiment an alternate control circuit arrangement is required. For example, if the oscillating scanning mechanism detects an object such as 79 at the upper-most extremity of its arc of oscillation, or the dotted position 77, illustrated in Fig. 6, but does not detect an object in the position occupied by the lower-most object 80 in Fig. 6, sui'ficient time delay must be provided so that upper nozzle 33' continues operation while scanning takes place below upper object 79. This time cycle must be coordinated with the speed of the object conveyor so that upper nozzle 33' operates only while an object 79'is within the effective areaof Referring to the details of Fig. 9, the scanning mecha-' nism is shown in the upper portion of its arc, in which position the presence of an object in the upper half of its travel will be detected, for example, the object 79 of Fig. 6. The presence of light upon photocell 43' creates a signal which is manifested in an electric current flowing along leads 81 and 82 to a snap action switch 83 having an actuating lever 84. The lever 84 is moved from'a first position to a second position by a cam 85 rigidly secured to the oscillating receiver housing 42, so that the switch is in position 1 during the upper half of its oscillation and in position 2 during the lower half of such oscillation. The positions referred to are illustrated by arcuate lines in Fig. 9, the point of changeover from position 1 to position 2 being a horizontal plane at the median of the arc of oscillation;

In position 1 of the switch 83, the photocell is connected through connection 86 to a relay circuit 66' having a threshold control 67', both of which may be of the type described previously in connection with Fig. 8. From the relay circuit, the balance of the control may be traced through connection 69' to a time delay circuit 68 having an adjustable period of delay through control 75, thence through connection 73' to solenoid air valve 74', each of these elements being of the type previously described in connection with Fig. 8. The valve 74 is used to control the operation or quiescenceof the upper nozzle 33' in Fig. 6.

An identical control system may be used to control the lower nozzle in Fig. 6 through the lower set of controls illustrated in Fig. 9, i.e., in position 2 of the switch connection of the photocell is established through lead 87 to relay circuit 66" having a threshold control 67' thence through lead 69" to time delay circuit 68" having an adjustable period of delay through 75", thence through connection 73" to solenoid air valve 74".

The alternate embodiment of Figs. 6, 7 and 9 discloses, therefore, a control system in which a single light transmitter, light receiver and photo-responsive device may be utilized in conjunction With a pair of spray nozzles to actuate either or both of the nozzles in response to the presence of an object within the coverage of the spray emitted from such nozzle or nozzles. The details of the means of oscillating the transmitter-receiver unit are not illustrated, but it is readily apparent that many mechanical means are available, as for example, an eccentric cam and follower or a crank and crank arm.

The foregoing embodiments are intended to be illustrative only of the various means for practicing the present invention, and their description will suggest alternative arrangements to those skilled in the art. Hence, it is intended that the invention be limited not by the disclosure thereof but only by the following claims.

I claim:

1. In a spray control operatively associated with means for moving objects to .be coated past a spray station and normally inoperative spraying means positioned to deliver coating material within a predetermined coating area so as to coat objects moving therethrough, the combination including; a light source positioned on one side of said objects to cast a beam of light upon the objects as they approach said coating area, light sensitive means disposed on the same side of said objects and arranged to intercept light reflected from a portion of said light beam by said moving objects, said portion of said light beam from which reflected light will be intercepted by said light sensitive means being spaced apart from said'coating area in a direction opposite to the direction of travel of the moving objects, meansresponsive to the presence of reflected light upon the .light sensitive means for causing the emission of coating mate- -rial from said spraying means.

2. In a spray control operatively associated with means for moving objects to be coated past a coating spraystation and normally inoperative spraying means positioned to deliver coating material within a predetermined coating area so as to coat objects moving therethrough, the combination including; a light source positioned on-one side of the path of travel of said objects to cast a relatively narrow, substantially non-divergent beam of light upon said objects as they approachsaid coating area, light sensitive means disposed on the same side of said objects and arranged to intercept light reflected from a portion of said light beam by said moving objects, said portion of said light beam from which reflected light will be intercepted by said light sensitive means being spaced apart from said coating area in a direction opposite to the direction of travel of the moving objects, means responsive to the presence of reflected light upon the light sensitive means for causing the emission of coating from said spraying means, and time delay means for continuing the spray for a predetermined time interval after passage of an object through said beam of light whereby a uniform coating is applied to the objects.

3. In a spray control operatively associated with means for moving objects to be coated past a coating spray station and normally inoperative spraying means positioned to deliver coating material within a predetermined coating area so as to coat objects moving therethrough, the combination including; a light source pivotally positioned upon a stationary upright member on one side of the path of travel of said objects to cast a relatively narrow, substantially non-divergent beam of light upon said objects as they approach said coating area, light sensitive means disposed in a vertically adjustable position on the same side of said objects and arranged to intercept light reflected from a portion of said light beam by said moving objects, said portion of said light beam from which reflected light will be intercepted by said light sensitive means being spaced apart from said coating area in a direction opposite to the direction of travel of the moving objects, means responsive to the presence of reflected light upon the light sensitive means for causing the emission of coating from said spraying means, time delay means for continuing the spray for a predetermined time interval after passage of an object through said beam of light, and mounting means including the aforesaid upright member rigidly supporting the spraying means, light source and light sensitive means whereby they may be adjustably positioned unitarily by moving the mounting means.

4. In a coating spray control operatively associated with means for moving objects to be coated past a coating spray station and a plurality of normally inoperative spraying means positioned to deliver coating material within a predetermined coating area so as to coat objects moving therethrough, the combination including; stationary mounting means positioned on one side of the path of travel of said objects, a plurality of light sources adjustably supported by said mounting means and arranged to cast relatively narrow, substantially non-divergent beams of light upon a predetermined vertical portion-of said objects as they approach said coating area, a plurality of light receiver means disposed in fixed positions relative to said stationary mounting means on the same side of the travel path of said objects and arranged in vertical juxtaposition to intercept light reflected from portions of said light beams by said moving objects, each of said receiver means being disposed to scan an area coexten sive with the vertical portion of the light beam emitted from a respective one of said light sources, said portions of said light beams from which reflected light will be intercepted by said light sensitive means being spaced apart from said coating area in a direction opposite .to the direction of travel of the moving objects, and means operatively associating each spraying means with one light receiver, said means being responsive tothe reception of reflected light and including means for causing the emission of coating from the spraying means associated therewith.

5. In a coating spray control operatively associated with means for moving objects to be coated past a coating spray station and a plurality of normally inoperative spraying means positioned to deliver coating material within a predetermined coating area so as to coatobjects moving therethrough, the combination including; a plurality of light sources adjustably positioned on a stationary upright member on one side of the path of travel of said objects and arranged to cast beams of light upon a predetermined vertical portion of said objects as they approach said coating area, a plurality of light receiver means disposed in vertically adjustable positions on the same side of the travel path of said objects and arranged in vertical juxtaposition to intercept light reflected from portions of said light beams by said moving objects, each of said receiver means being disposed to scan an area coextensive with the vertical portion of the light beam emitted from a respective one of said light sources, said portions of said light beams from which reflected light will be intercepted by said light sensitive means being spaced apart from said coating area in a direction opposite to the direction of travel of the moving objects, means operatively associating each spraying means with one light receiver, said light receiver being responsive to the reception of reflected light and including means for causing the emission of paint from the spraying means associated therewith, and a common stationary supporting member for the light sources, spraying means and light receiver means.

6. In a coating spray control operatively associated with means for moving objects to be coated pasta coating spray station and normally inoperative spraying means positioned to deliver coating to said objects, the combination including; a light source mounted upon a fixed pivot on one side of said objects and oscillatable about said pivot to cast a moving beam of light upon a path lying in a vertical plane transverse to the path of motion of said objects and longitudinally spaced fromthe spraying means, light receiver means oscillatable with said light source and including a restricted light admission port having a field of view including the aforesaid path of the light beam, said receiver being arranged to intercept light reflected from said objects, and means responsive to the presence of reflected light in the light receiver means for causing the emission of coating from said spraying means.

7. Apparatus according to claim 6 in which a pair of vertically juxtaposed nozzles are selectively caused to emit paint in response to light reflected from objects passing within the range of one or both nozzles.

8. Apparatus according to claim 6 including a .com- -mon mounting means for the spraying means and oscillatable light source and light receiver means whereby movement of the mounting means unitarily moves the means mounted thereon.

9. A spray station comprising; a spray booth having .a front portion and a back wall; a conveyor adapted to move objects longitudinally through the spray station along a plane disposed substantially medially between the aforesaid front portion and back wall; a light source disposed adjacent the front portion of the spray station and arranged to light a confined portion of said spray booth including vertical segments of the aforesaid back wall and substantially medially disposed plane; .a light responsive receiver means disposed adjacent said front portion and having a confined opening adapted to intercept light reflected from a portion of said light beam by said moving objects and to exclude light reflected from the back wall of the spray station; coating spraying means adjacent said front portion and arranged to deliver coating material within a predetermined coating area, said coating spraying means being further operatively associated with and adapted to be initiated and terminated by the presence of reflected light in said receiver means; said portion of said light beam from which reflected light will be intercepted by said light sensitive means being spaced apart from said coating area in a direction opposite to the direction of travel of the moving objects.

10. A spray station comprising; a spray booth having a front portion and a back wall; a conveyor adapted to move objects longitudinally through the spray station along a plane disposed substantially medially between the aforesaid front portion and back wall; a light source oscillatably mounted adjacent the front portion of the spray station and arranged to light a confined portion of said spray booth including vertical segments of the aforesaid back wall and substantially medially disposed plane; a light responsive receiver means mounted to oscillate with said light source and having a confined opening adapted to intercept light reflected from a portion of said light beam by said moving objects and to exclude light reflected from the back wall of the spray station; and paint spraying means adjacent said front portion and arranged to deliver coating material Within a predetermined coating area, said coating spraying means being further operatively associated with and adapted to be initiated and terminated by the presence of reflected light in said receiver means; said portion of said light beam from which reflected light will be intercepted by said light sensitive means being spaced apart from said coating area in a direction opposite to the direction of travel of the moving objects.

References Cited in the file of this patent UNITED STATES PATENTS 2,488,519 Andrews Nov. 22, 1949 2,529,291 Graham Nov. 7, 1950 2,731,110 Woolard Jan. 17, 1956 2,781,020 Scott Feb. 12, 1957 2,797,171 Fralish June 25, 1957 

